Hooking Empty to a Plane
I don't know where you failed, but according to your blend ...
You created a vertex group &quot;hook&quot;, but you didn't Assign two top vertices to this group.

When you Assign two top vertices to Plane, position Empty on top Plane's edge, add Hook modifier, set Object &gt; Empty and Vertex Group &gt; hook

Than Duplicate Plane (so you don't have to set modifier for each) and change Strenght value for each 1 / 0.8 / 0.6 / 0.4 / 0.2
Now when you move Empty along Y axis bars are scaled accordingly ...